1. Field of the Invention
The invention relates to large machines having relatively rotatable upper and lower structures. More particularly, the invention relates to draglines.
2. Discussion of Prior Art
A walking dragline typically includes an upper structure and a boom which extends upwardly and outwardly from the upper structure and which has thereon a sheave for supporting a hoist rope. The hoist rope extends over the sheave to a bucket for causing vertical movement of the bucket. A drag rope is connected to the bucket for causing horizontal movement of the bucket. The upper structure is supported by a tub that sits on the ground when the dragline is engaged in digging operations. The upper structure is rotatable relative to the tub about a vertical pivot axis. A pair of walking mechanisms are mounted on the opposite sides of the upper structure and are operable for moving the dragline over the ground between digging operations.
Historically, heavy equipment such as draglines with rotating upper structures have had minimal clearance between the upper rotating structure and the top of the lower support structure when employing a flat top for the lower structure. This has made maintenance of equipment in that area, such as the mechanical and electrical equipment involved with rotating the upper structure relative to the lower structure, a difficult task. Improving human access in this area would allow the user of the equipment to more easily inspect, maintain, and repair the rotating machinery and any other equipment that may be located in the area. Some machines have structural elements added to the bottom surface of the upper deck. These elements often result in cracking problems with the main structure due to the method of attachment.